OhmJS

@ohmjs.org

A user-friendly parsing toolkit for JavaScript and TypeScript ∙ https://ohmjs.org

Line chart showing weekly downloads for the npm package "ohm-js" from February 28, 2025 to February 26, 2026. The graph displays relatively flat growth at around 200,000 weekly downloads for most of the year, then shows dramatic exponential growth starting in late January 2026, skyrocketing from approximately 200,000 to 1.8 million weekly downloads by late February 2026. The y-axis shows weekly downloads ranging from 0 to 1.8M, and the x-axis shows dates with major tick marks every few months

Ohm: A Parsing Toolkit for JavaScript and TypeScript — It’s been a few years since we covered this project and it’s come along a lot since. It’s a library for building PEG-based parsers you can use in interpreters, compilers, analysis tools, etc. and you can even play with its grammar online.

Warth, Dubroy, et al.

$Screenshot of the following code: // In abstract algebra, a _monoid_ is a set (or a data type) that has // (a) a "combine" operation that's associative, i.e. (a + b) + c = a + (b + c) // (b) an identity or neutral element. // This is our identity element… const LOC_IDENTITY = {line: 0, col: 0}; // …and this is our "combine" operator. function sumLocations(a, b) { return { line: a.line + b.line, // If `b` has more than one line, we can ignore `a.col`. col: b.line > 0 ? b.col : a.col + b.col, }; } function compareLocations(a, b) { return a.line - b.line || a.col - b.col; } const semantics = g.createSemantics(); // A helper operation to get the "size" of a node, such that // endLoc = sumLocations(startLoc, size). semantics.addAttribute('_size', { _default(...children) { return children.reduce((acc, node) => sumLocations(acc, node._size), LOC_IDENTITY); }, _terminal() { const lines = this.sourceString.split('\n'); return { line: lines.length - 1, col: lines.at(-1)?.length || 0, }; }, });$